Results from a very small, very early study suggest that some women diagnosed with advanced-stage breast or ovarian cancer got some benefits from an experimental vaccine that targets breast and ovarian cancer cells.

The cancers had stopped responding to standard treatment options.

The results were published in the Nov. 15, 2011 issue of the journal Clinical Cancer Research.

Vaccines protect people around the world from many life-threatening infections. Vaccines generally work by exposing a person's immune system to parts of dead or weakened bacteria or viruses. This exposure makes the immune system react as if the body had the real infection and develop defenses. Later, if the body is naturally exposed to the disease-causing bacteria or virus, the immune system releases the defenses and stops the infection from ever taking hold.

Doctors have been investigating if a vaccine could help protect a person from cancer or help a person battle cancer. These experimental vaccines usually contain the same proteins that are in the cancer cells. The vaccines may also contain other agents that stimulate (wake up) the immune system. Experimental cancer vaccines may be given as a shot in the arm or as injections directly into the cancer tissue.

PANVAC, the experimental vaccine discussed in this article, was first developed to treat advanced-stage pancreatic cancer (the name comes from PANcreatic VACcine). PANVAC was designed to stimulate the immune system to react to two substances: carcinoembryonic antigen (CEA) and mucin-1. Pancreatic and other cancer cells, including some breast cancer and ovarian cancer cells, usually have high levels of CEA and mucin-1. A weakened version of a pox virus (like the viruses that causes chicken pox and smallpox) in PANVAC is programmed to produce CEA and mucin-1, which stimulates the immune system to hopefully attack cancer cells that are making the same substances. PANVAC also contains agents that can stimulate the immune system's overall reaction to the vaccine.

A total of 26 women were in the PANVAC study (12 women were diagnosed with metastatic breast cancer and 14 were women diagnosed with metastatic ovarian cancer). The women were in the study for one of two reasons: the cancer had grown while a woman was getting standard treatments or a woman couldn't be treated with any more standard treatments because of her overall health. The women got monthly PANVAC injections.

The 12 women diagnosed with breast cancer lived for 1 month to more than 3 years before the cancer showed signs of growing (progression-free survival). Half the women lived for at least 2.5 months before the cancer grew. The women lived for nearly 2.7 months to nearly 4 years whether or not the cancer showed signs of growing (overall survival). Half the women lived for more than a year whether or not the cancer showed signs of growing.

The 14 women diagnosed with ovarian cancer lived for 1 month to 6 months before the cancer showed signs of growing. Half the women lived for at least 2 months before the cancer grew. The women lived for 1.5 months to nearly 5 years whether or not the cancer showed signs of growing. Half the women lived for more than 15 months whether or not the cancer showed signs of growing.

This very early study didn't include comparison groups (similar women who didn't get vaccine), so it's not absolutely certain that the vaccine helped weaken the cancer. Still, because some of the women lived for a long time with no other treatment, whether or not the cancer grew, it suggests that PANVAC may be a useful treatment option for women with advanced-stage breast or ovarian cancer.

Much more research is needed before doctors can confidently understand if, for whom, and when a vaccine such as PANVAC may be useful in a breast or ovarian cancer treatment plan.

If you're being treated for advanced-stage breast cancer, you and your doctor may be considering a number of options, especially if the cancer has stopped responding to standard treatments or you can no longer tolerate such treatments. An experimental treatment, such as PANVAC, may still be an option if you're willing to participate in a clinical trial. Ask your doctor if there are any clinical trials that might be a good fit for you and your unique situation. Visit the Breastcancer.org Clinical Trials pages for more information.